feat: support Chinese nickname in registration

- User input "昵称" stored in `name` field (supports Chinese)
- `username` auto-generated (PocketBase requires ASCII)
- Password rules displayed inline with real-time validation
- All UI displays prefer `name` over `username`

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/components/game/GameComments.vue

@@ -71,7 +71,7 @@ function formatDate(dateStr: string) {
     <div v-else class="comment-list">
       <div v-for="c in comments" :key="c.id" class="comment-item">
         <div class="comment-header">
-          <span class="comment-author">{{ c.expand?.author?.username || '用户' }}</span>
+          <span class="comment-author">{{ c.expand?.author?.name || c.expand?.author?.username || '用户' }}</span>
           <span v-if="c.rating" class="comment-rating">
             <el-icon v-for="i in c.rating" :key="i" :size="12"><StarFilled /></el-icon>
           </span>